1. Field of the Presently Disclosed and/or Claimed Inventive Concepts
The inventive concepts disclosed and claimed herein relate to instruments for fixing orthopedic implants, and more particularly, but not by way of limitation, to an apparatus for dispensing multiple implants and applying a counterforce.
2. Brief Description of Related Art
Several techniques and systems have been developed for correcting and stabilizing the spine and for facilitating fusion at various levels of the spine. Stabilization of the spine for various conditions, including degenerative disk disease, scoliosis, spondylolisthesis, and spinal stenosis, often require attaching implants to the spine and then securing the implants to spinal rods. Such spinal fixation devices can immobilize the vertebrae of the spine and can alter the alignment of the spine over a large number of vertebrae by connecting at least one elongate rod to the sequence of selected vertebrae. These rods can span a large number of vertebrae, such as three or four. The spine anatomy, however, rarely allows for three or more implants to be directly in line. In order to allow for this irregularity, the rod must be contoured to the coronal plane.
Spinal fixation has become a common approach in fusion of vertebrae and treating fractures and the above listed spinal disorders. A common device used for spinal fixation is a bone fixation plate assembly. Typical bone fixation plate assemblies have a relatively flat, rectangular plate with a plurality of apertures therethrough. Another option is an implantation fixation system that locks a rod to several vertebrae. In these systems, as with other spinal fixation systems, various fasteners, such as bone screws, are used to secure the implantation fixation assembly to the desired and targeted vertebrae of the patient. These screws vary in design and shape depending upon their desired location and use.
Polyaxial locking screws are frequently used as fasteners in implantation fixation systems. Once these screws are set in a desired position, the screws are securely fixed in that position to minimize or eliminate movement of the screws. This is typically accomplished with a fixation system that securely engages the polyaxial screw.
There are numerous polyaxial screws and fixation systems existing in the market today. Some fixation systems utilize a rod receiving head having a central passage, and a polyaxial screw inserted into the central passage. The screw has a head portion that seats inside one end of the rod receiving head, and a threaded shank that projects through the end of the rod receiving head in an exposed manner. An elongated rod is seated in the rod receiving head and extends transversely through the central passage. The rod is secured in the rod receiving head with a threaded locking cap that is screwed around the exterior of the rod receiving head or in the interior of the rod receiving head to lock the rod in place.
Locking caps are typically inserted into the rod receiving head with an instrument that has been loaded with a single locking cap. Consequently, after one locking cap is threaded into the rod receiving head with the instrument, a surgeon is handed another instrument loaded with another locking cap, or the same instrument is passed to a technician who loads the same instrument with another locking cap and passes back to the surgeon. The application of the locking caps continues in this back and forth fashion until all the locking caps are threaded and secured into position, and thus the application of the locking caps is a time consuming process.
Another characteristic of the locking cap application process is that the torque applied to the locking caps is transferred to the rod receiving head and polyaxial screw. More specifically, a significant amount of torque is typically applied in the final tightening. This introduces a risk of “blowout,” in which torque or other components of force tilt the shank out of its set alignment in the screw hole causing the shank to break through the relatively thin bone wall of the pedicle. In such a case, removal and resetting of the polyaxial screw can exacerbate the trauma to the bone.
To control the risk of blowout, some practitioners use additional instrumentation to apply a countertorque to the fixation mechanism, so that the torque applied to locking cap does not cause rotation or displacement of the locking cap and polyaxial screw. This requires the careful balancing of torque with countertorque, and any imbalance can still cause blowout. Moreover, application of countertorque requires an additional instrument to be used at the same time that the locking cap is being driven into the cage. Aside from the obvious disadvantage of adding to instrument costs and instrument preparation, the countertorque instrument can be cumbersome to use while advancing the locking cap at the same time.
To this end, a need exists for an improved apparatus and method for delivering multiple locking caps while minimizing the time associated with handling and tightening such locking caps during surgery. It is to such an apparatus and method that the inventive concepts disclosed and claimed herein are directed.